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1. Field of the Invention
The present invention relates to improvements in article conveyance systems having roller bed assemblies frictionally powered by plastic driver pads carried on a chain drive mechanism.
2. Description of the Prior Art
Abell U.S. Pat. No. 4,588,073, and Wiggers and Alderink U.S. Pat. No. 5,176,246 (both owned by the assignee of this invention) disclose padded chain drives for roller conveyors. In these conveyors, the pads are moved into engagement with the rollers to drive the rollers and advance articles on the conveyor and are disengaged from the rollers when the conveyor is not moving articles. The pads are positioned on the chain link drive and advance with the drive chain. Geib U.S. Pat. No. 5,984,082 also is directed to a padded chain drive for a roller conveyor.
The pads conventionally are resilient, thermoplastic polyurethane elastomers. As such, they are subject to wear from frictionally engaging the rollers. Thus the pads require periodic maintenance and replacement. However, it has always been difficult to determine when the driver pad has worn enough to require replacement. The common practice is to use calipers or height gauges to measure the driver pad height and thus determine when the minimum height is reached when replacement is required. Both of these processes are difficult to use, particularly the calipers, and both measure only in one place and not over the entire length of pad. Since the chains and pads extend for hundreds of feet in some conveyors, it is apparent that it is difficult, if not virtually impossible to be sure the measurement has been made at the thinnest place, i.e., the place where the pad is most likely to fail.
Accordingly it is a principal object of this invention to provide a driver pad which has a built-in system for determining wear on the pad. This is achieved in the present invention by co-extruding the driver pad with a visually distinct wear element embedded in, the same composition as, and integral with the remainder of the polymer pad, but preferably of a different color.
The majority of the pad is of one color and the visually distinct wear element part of the pad is of a distinctly different color. The colored portion. preferably is substantially triangular in shape with the base of the triangle oriented toward the conveyor rollers. The sides of the wear element converge toward each other in the pad when viewed in cross-section. Thus, the width of the colored surface indicates the relative wear on the driver pad and if there is no color present, the pad needs replacement.
Since the colored segment extends the entire length of the pad and chain, one can observe the entire pad from a single viewing point while the chain is moving. Alternatively, once can walk the length of the pad and observe its total condition by visual observation.